In current digital display systems employing spatial light modulators, lamps with intensive luminance but compact size are dominantly used as light sources of the display system. Arc lamps with short arc lengths are a group of such lamps. For example, an arc lamp with the arc length of 0.7 mm or 1.0 mm has a higher brightness than an arc lamp with an arc length of 1.3 mm or 1.6 mm, because the beam produced by smaller arc length lamps can be more easily passed through an optical system.
However, arc lamps in digital display systems prefer spatial light modulators with selected dimensions in favor of high optical efficiencies of the display systems. Specifically, for an arc lamp with a given arc length, it is desired for the spatial light modulator to have a large enough size—if the optical efficiency of the projection system (or more specifically, the optical coupling efficiency, to which the brightness of images produced by the spatial light modulator, of the light source to the array) is not to be degraded. A large spatial light modulator, however, is not cost-effective due to many factors, such as higher costs in manufacturing and optical elements (e.g. condensing and projection lenses). In practical design of the display system and the spatial light modulator, the cost-effectiveness and the optical efficiency need to be balanced—yielding an optimal size of the spatial light modulator.
The diameter of a spatial light modulator is proportional to the pixel pitch (defined as the center-to-center distance between adjacent pixels of the spatial light modulator) for a given resolution (defined as the number of pixels in the spatial light modulator) of the pixel array. Given a spatial light modulator with optimum size, the pixel pitch needs to be reduced if a higher resolution is desired. Because the pixel pitch is a summation of the gap between adjacent pixels and the size of the pixel, reduction of the pixel pitch requires reduction of the gap between adjacent pixels if fill factor (the percentage of reflective area to total array size and measured by a ratio of the pixel size to the pitch) is not to be lost.
However, reducing the pixel pitch (or the pixel size) to gain higher resolution in a spatial light modulator with given size is not a trivial task. For example, many of current micromirror-based spatial light modulators carry micromirrors each having a reflective deflectable mirror plate and two addressing electrodes for deflecting the mirror plates. Reduction the pixel pitch in a micromirror array certainly requires reduction of the pixel size when the gaps between adjacent pixels reach their limits. Reduction of the micromirror device size involves both of reductions of the mirror plate size and the size of the addressing electrodes, as well as the circuitry associated with the addressing electrodes. When the micromirror has two or more addressing electrodes, reducing the size of the addressing electrode becomes more difficult and even impossible with current fabrication technologies. Moreover, interference between the multiple addressing electrodes increases as the sizes and neighboring distances of the multiple addressing electrodes are reduced.
Therefore, what is needed is a spatial light modulator having an array of micromirror devices and a method of making such a spatial light modulator that allows for higher resolutions while maintain the same optimum size.